USB hubs are USB connectors that extend a USB interface to multiple (typically 4) devices that can be used at the same time.

USB hub is divided into: active, passive, hybrid three kinds.

Active: The connection of the network media on the signal has the effect of regeneration and amplification, so that the length of the connected media to reach the maximum effective length, USB Hub need to have power to work, the current majority of the hub for this type.

Passive: Only act as a connector, do not need power to work, the market is already rare.

Hybrid: Can connect many types of cable, such as shaft and twisted pair.

The USB hub consists of a USB hub forward repeater and a USB hub controller. The USB hub forwarding repeater is responsible for connection work. USB Hub It also supports exception handling such as bus error detection and recovery, connectivity, and connectionless detection. The USB hub Controller provides a communication mechanism for the host to the USB hub. USB Hub-specific state and control commands allow the host to configure the USB hub and monitor and control each of its downlink ports.

USB hubs Show different connection behavior depending on whether they are transmitting packets, waking signals, or being idle. Packet signal connection. Packet signal connection is divided into upstream connection and downlink connection two kinds. The uplink connection is host-oriented. USB Hub When an enabling Downlink Port detects a sop, an upstream connection is established that is only to the upstream port and not to any other downlink port. The downlink connection is device-oriented. When the SOP is detected on the uplink port, the USB hub is established to all connections that enable the downlink port. The port that is not in the enabling State cannot be transmitted in the downlink direction. The USB hub also has an idle state with no connections. All ports in the USB hub are in receive mode while idle, USB Hub waiting for the start of the next package. Second, wake up connection. The pending USB hub sends the wake signal received by the uplink port to all enabled downlink ports. When the pending USB hub detects the arrival of a local suspend or enable a wake signal to the downlink port, the reflection wakes up to the uplink port and all the enabling downlink ports including itself. The wake-up signal is not reflected to the failed or pending downlink port. USB Hub A more detailed discussion will follow.

A USB hub is a very important USB component that connects the host and the device. It is important to detect and prevent any connection errors, especially those that can cause deadlocks. The USB hub must handle connection errors in forwarding mode. USB hubs must also be able to detect and recover packages destined for USB hub controllers. USB Hub Each USB hub has a frame timer. Its time comes from the local clock of the USB hub and synchronizes with the host via the SOF from the host. It provides a time reference that is used to detect idle (babbling) devices and prevent USB hubs from being set to an invalid uplink USB hub. The USB hub must keep track of the host frame cycle and be able to remain synchronized even if the two consecutive SOF tokens are lost. USB Hub The frame timer is not synchronized after the reboot or wake up. As long as two consecutive SOF packets are received, it must be synchronized.